Air in CH system...but why?

[amfisted]

Well, my plan to add new inhibitor to the F and E tank of our conventional heating system didn't quite go as I expected.

I tied up the tank ball valve, drained the system to an outside gully via the drain valve on a radiator by the back door (we live in a bungalow) closed the radiator drain valve, added inhibitor to the F and E and refilled the tank and system. I bled the rads (none of which had any air in, perhaps a warning sign) turned on the heating and the boiler started gurgling like there was no tomorrow. The pump was making unusual noises too, and eventually the boiler locked off with a low water pressure fault (F22 on a Glowworm Flexicom).

I was at a loss to work out what I'd done wrong, but my missus came to the rescue, locating a clip on Youtube which described how to bleed air from the system via a drain cock just below the pump. The subsequent removal of air has brought the boiler back to life, although its still gurgling.

I noticed in the Wiki a reference to a lever on the pump that you can use to switch to "manual" when bleeding. The only lever I can see ( by using a mirror) is on the body of the pump on the hidden side next to the cylinder, and it seems to have three settings marked with one, two and three horizontal lines. Would that be the relevant switch, and which setting is manual? Its on the setting with three lines at the moment.

What did I do wrong to introduce so much air into the system?

 

[terryplumb]

If you drain water out of the system ,it fills with air ,naturally.
The pump switch is for the speed of the pump ,nowt to do with draining air.

 

[oldbuffer]

1. If you drained the system without emptying the F&E tank, then you've let any muck in the F&E flow through the system.
2. The switch you refer to is more likely on the motorised valve(s) than on the pump.
3. The pump is normally bled by removing the big screw in the centre of the pump body. Needs old rags handy, and don't drop / lose the screw.
4. You may well have drained the coil in the hot water cylinder as well as the central heating circuit. If you have an air vent on the upper inlet to the coil, open it to let air escape. If its an automatic air vent, they usually leak and someone is likely to have screwed the top cap down. Undo cap, release air, do up again.
5. When bleeding:
5a. Run the system (CH and HW) for a few minutes.
5b. Turn off and leave for 10 minutes or so.
5c. Bleed from the lowest point upwards, although most of the air will be at the highest point.

 

[amfisted]

Thanks for the replies. I'll leave the 3 setting lever alone.

I drained and cleaned the F&E tank yesterday, but I suppose its possible some of the muck was stirred up and went down the feed pipe from the tank.

I tried bleeding the large screw in the centre of the pump, but no air came out. Air was only expelled when I opened the valve below the pump, and that seems to have helped. I'm at a loss as to how to drain above the places I've drained already, and although there are AAVs in the loft they don't appear to be operating because I can't hear any air being expelled. Is there a way of releasing the air manually from an AAV?

I'll have a look at the cylinder and see whether I can find a vent.

 

[Nige F]

I noticed in the Wiki a reference to a lever on the pump that you can use to switch to "manual" when bleeding. .

?

There is a lever on mid position valves like that.

 

[Gasguru]

It sounds like all the overhead pipework in the roof is still full of air.
AAVs are nearly always useless...they either block or leak.
Far better are manual air vents.
Either replace the AAVs or fit manual air vents using a 15mm compression to 1/2 female thread with a 1/2 radiator vent. These will be the most reliable manual vent.
You lock the lever on the mid position valve to open the valve whilst draining and filling.
Turn the gas off at the meter until the pump is quiet and the system is free of air...no point in killing the boiler off. You might need to reset the boiler a few times when it fails to ignite.

 

[amfisted]

Thanks again.

Reckon I’ll head up to the loft, crack the joint on the AAV and see if that releases any air. Whether that works or not I’ll do as you suggest and bin it, because it’s clearly not doing the job it was fitted for, and I’ll replace it with a manual valve.

 

[amfisted]

I’ve ordered the bits from Sfix so that I can make up two manual vents today.

Gasguru, can you please explain what you mean by locking the lever on the mid position valve? I assume you mean the diverter valve, which has a small lever currently set to the right of its slot. Should this lever be moved to a different position during draining and filling?

The other thing I've noticed is that when the boiler was heating the water this morning the gurgling noise ( which has decreased substantially but is still irritatingly audible) is coming from the Magnaclean filter above the boiler and not the boiler itself. I don't suppose it really matters because it still indicates that there's air in the system.

 

[Mottie]

Sometimes I found with my old vented system, putting the pump on speed 3 helps push the air out of the pump and around to the rads and it can then be bled out more easily.

 

[amfisted]

The pump is already on speed 3, but thanks anyhow for the suggestion.

 

[Gasguru]

Stick the speed back to its original setting....I doubt it needs to be on 3.
I doubt you have a diverter valve...more likely a mid position valve ie. the valve can adopt 1 of 3 positions...heating only (rads), hot water (cylinder) only or a mid position where both circuits are heated.
The lever when locked into the notch sets the valve in this mid position allowing water to flow to (or from) all circuits during re-filling and draining. After that procedure the valve is unlocked to enable normal operation.
The Magnaclean has a bleed screw on the top.

 

[amfisted]

Stick the speed back to its original setting....I doubt it needs to be on 3.
I doubt you have a diverter valve...more likely a mid position valve ie. the valve can adopt 1 of 3 positions...heating only (rads), hot water (cylinder) only or a mid position where both circuits are heated.
The lever when locked into the notch sets the valve in this mid position allowing water to flow to (or from) all circuits during re-filling and draining. After that procedure the valve is unlocked to enable normal operation.
The Magnaclean has a bleed screw on the top.

Thanks once more for the information.

I did as you suggested and made a manual valve out of 15mm compression, half inch female thread and a rad vent. Once fitted I opened the vent and a fair bit of air came out, so that may well solve the problem. There's a second AAV but it doesn't have an isolating valve below unlike the one I've just removed, so to change it I'd have to drain the system again, something I'm reluctant to do.

No air was expelled from the Magnaclean when I opened the bleed screw, so I'm hoping the manual valve will deal with what's left.

 

[Gasguru]

Just snatch it...towels and swap it quick. Presumerably the F&E cistern is only marginally higher than the vent so the pressure will be minimal.

 

[amfisted]

I might give it a shot, “finger in the dyke” and all that.

That AAV is at least 3 feet below the F&E, which prompts me to ask:would the air be collected more effectively if I put the manual vent on top of a longer piece of pipe, say 600mm? To do this I’d have to bend the pipe to follow the profile of the roof slope, so it wouldn’t be vertical, more like 45 degrees.

 

[amfisted]

This post purely for the information of anyone who was good enough to contribute to this discussion and provide me with advice.

In the end, I didn't find that the situation had been noticeably improved by changing the AAVs for manual vents. So I fitted a brand new AAV which I knew was working, and it seems to have removed the majority of the remaining air because the boiler is now much quieter.

Thanks again all for giving your thoughts.